This invention relates to an electrical sub-assembly having a lead frame to be compressed between a circuit board and a heat sink to enhance heat transfer from an inter-connecting substrate to the heat sink.
Lead frames and thick film circuits have been advantageously employed with respect to heat conducting, electrically insulating substrates. In many constructions, a lead frame sub-assembly is placed upon solder paste or conductive epoxy located on the insulating substrate. The intervening solder or epoxy is reflowed by heat or other means to permanently bond portions of the lead frame sub-assembly to the substrate. In addition, other discrete components may be placed upon certain portions of the lead frame sub-assembly or upon portions of the thick film circuit and permanently bonded thereto by reflowing the interconnected solder paste or conductive epoxy. Portions of the lead frame sub-assembly may be detached so that a sub-assembly is formed which includes the insulating substrate and a series of lead frame portions which are each bonded to the substrate by the reflowed solder or conductive epoxy. Portions of the lead frame may be bent normal to the substrate to form electrical terminal connections which may function to conduct large amounts of current to operating circuits which may include various components such as high power conducting semi-conductor devices. Such construction is particularly useful in high power energy conversions such as employed with electric motor drives or the like. One highly desirable construction is shown in the U.S. Pat. No. 3,958,075 entitled "High Power Thick Film Circuit With Overlapping Lead Frame", which issued on May 18, 1976 to Lance R. Kaufman.
In one desirable construction, one or more lead frame connectors are bonded to a pair of spaced substrates lying in the same plane with the lead frame connectors thereafter bent into U-shaped configurations so that one portion of each lead frame connector and attached substrate is spaced in parallel with another portion of the lead frame connector and attached second substrate. Such construction has been found to be highly desirable in positioning a photon emitting control element in spaced relationship with a photon activated switch operating in a solid state power control device, such as shown in the U.S. Pat. No. 4,156,148 entitled "Photo-coupling Structure For A Solid State Power Control Device", which issued on May 22, 1979 to Lance R. Kaufman.
Sub-assemblies including lead frames attached to an insulating substrate have been advantageously placed within an insulating housing. Such housings have included a cavity surrounded by one or more edges which engage the substrate to limit its depth of entry into the cavity. The use of such limiting edge avoids pressure being placed upon the circuit elements to permit thermal contraction and expansion of the circuit elements in response to heat generated by the conducted electrical energy. Such thermal expansion and contraction is particularly desirable in high power conducting solid state devices such as thyristors or the like. One highly desirable device is shown in U.S. application Ser. No. 834,601 entitled "Power Switching Device Having Improved Heat Dissipation Means", which was filed on Sept. 19, 1977 by Lance R. Kaufman.
Plural electrically insulating substrates each containing respective interconnected lead frame connectors have been advantageously employed within a compact circuit package. Under certain conditions, selected lead frame connectors which are mounted to one substrate engage selected lead frame connectors mounted to another substrate at or within housing apertures providing external electrical connection to such lead frame connectors. One desirable construction is shown in U.S. Pat. No. 4,218,724 entitled "Compact Circuit Package Having Improved Circuit connectors", which issued on Aug. 19, 1980 to Lance R. Kaufman.
Compact circuit packages are capable of retaining a wide variety of circuit constructions mounted upon one or more of the substrates. By way of example, an electrical power converting thyristor firing circuit could be used, such as disclosed in U.S. Pat. No. 4,257,091 entitled "Electrical Power Converter Thyristor Firing Circuit Having Noise Immunity", which issued on Mar. 17, 1981 to Lance R. Kaufman. Optically couplable circuit elements could be used as shown in U.S. Pat. No. 4,266,140 entitled "Positioning Means For Optically Couplable Circuit Elements", which issued on May 5, 1981 to Lance R. Kaufman. One or more terminals could be used for the main input and output power connections such as disclosed in U.S. Pat. No. 4,215,235 entitled "Lead Frame Terminal", which issued on July 29, 1980 to Lance R. Kaufman. One or more variable resistance devices could be used such as disclosed in U.S. Pat. No. 4,250,481 entitled "Variable Resistance Device For Thick Film Circuitry", which issued on Feb. 10, 1981 to Lance R. Kaufman. One or more dual resistor elements could be used such as disclosed in U.S. Pat. No. 4,196,411 entitled "Dual Resistor Element", which issued on Apr. 1, 1980 to Lance R. Kaufman. Numerous other circuits and elements could also be utilized.